1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Electron orbitals?

  1. Apr 12, 2013 #1
    Hey all,
    Why do electron orbitals exist? That is to say, why do electrons in essence move away from the proton (potential) instead of attempting to get closer to the proton? Feel free to throw out some quark and nuclear physics...haven't had qed yet.

  2. jcsd
  3. Apr 12, 2013 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Quark and nuclear physics?

    We don't even need to go that far. Have you had 1st year quantum mechanics?

  4. Apr 12, 2013 #3
    For the sake of argument lets assume I haven't. If you liken this to a potential well, I get it, more energy higher orbital. But that's a model, I'm arguing semantics. Why when an electron absorbs a corresponding photon does it act as if repelled into a higher orbital? I guess you can interpret my question as Bohr's problem, why doesn't the electron fall onto the proton?
  5. Apr 12, 2013 #4
    To get started:

    Think of a violin string as an analogy: the ends are constrained, so it can have only certain tones...certain vibrational patterns and associated energies. it's energy levels are constrained to certain values...it's degrees of freedom are limited when the degrees of freedom are limited.

    Another helpful analogy is to think of the electron as a wave....when it's in free space the wave is [almost] everywhere, it extends all over the place. But when attracted by a proton in a nucleus, for example, that wave is now localized...it's constrained and so its different from the free space case. And the constraint is also modified by the presence of other electrons and additional protons. Since the energy is contained in the wave, changing it's configuration via the presence of nearby particles changes the wave characteristic and likely energy levels. It's very unlikely for the electron to be found between allowed energy levels.

    In contrast, a [truly] free electron can take on any energy level. But when it is part of an atom or a larger structure, it's constrained...it's degrees of freedom are determined and limited by the whole structure. [ Just like you cannot stand up if I place you in a small square box.]
    So an electron's energy levels and degrees of freedom are determined by the numbers of protons in the nucleus as well as the particular structure of a lattice, as examples. The Schrodinger wave equation describes these.

    For a 'particle' to absorb a photon you need internal degrees of freedom which can be excited. Complex particles can do this; elementary particles [w/o constitutent components] cannot. A free electron can't absorb a photon since it has no inner degrees of freedom. An electron bound in an atom can because the whole atom (proton-electron bound state) provides these inner degrees of freedom.

    Electrons behave very differently in different bound states....because their energy levels are constrained by their surroundings. They take on different apparent masses, different sizes, etc, whether in an atom, a lattice, and especially graphene where they appear to have virtually no mass...!! If you place an electron in a potential well, it takes on the size of the 'enclosure'...and is thereby constrained; only certain standing waves are 'allowed'....those with zero amplitude at the boundaries.

    Wikipedia has a decent,short explanation:


    This means the probability density of an electron in a nucleus of, say, hydrogen, is zero.

    My favorite explanation of a particle:

    Why particles exist, why we have the particles we observe, why they have certain characteristics and not others, why all particles exhibit wave particle duality, is because...well, it's just that way!
    Last edited: Apr 12, 2013
  6. Apr 12, 2013 #5


    User Avatar

    Staff: Mentor

    It is not zero for s electrons.
  7. Apr 12, 2013 #6


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Please read our FAQ subforum.

    https://www.physicsforums.com/forumdisplay.php?f=209 [Broken]

    Last edited by a moderator: May 6, 2017
  8. Apr 12, 2013 #7
    Thanks for all the feedback everyone!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook